Heretofore, a fuel cell system including a fuel cell for receiving the supply of a reactant gas (a fuel gas and an oxidizing gas) to generate a power has been suggested and put to practical use. Moreover, in recent years, a fuel cell system has been suggested in which a variable gas supply device such as a mechanical variable regulator or an injector is provided in a fuel supply flow path for allowing a fuel gas, which is supplied from a fuel supply source such as a hydrogen tank, to flow to the fuel cell, whereby the supply pressure of the fuel gas from the fuel supply source can be changed in accordance with the operation state of the system (e.g., see Japanese Patent Application Laid-Open No. 2005-302563).